You can't specify target table for update in FROM clause

mysql中You can't specify target table for update in FROM clause错误的意思是说，不能先select出同一表中的某些值，再update这个表(在同一语句中)。 例如下面这个sql：

代码如下:

delete from tbl where id in (        select max(id) from tbl a where EXISTS        (            select 1 from tbl b where a.tac=b.tac group by tac HAVING count(1)>1        )        group by tac)

改写成下面就行了：

 代码如下:

delete from tbl where id in (    select a.id from     (        select max(id) id from tbl a where EXISTS        (            select 1 from tbl b where a.tac=b.tac group by tac HAVING count(1)>1        )        group by tac    ) a)

也就是说将select出的结果再通过中间表select一遍，这样就规避了错误。注意，这个问题只出现于mysql，mssql和oracle不会出现此问题。